The purpose of this project is to determine the minimal infectious dose of HIV-2287 in Macaca nemestrina inoculated by mucosal routes. The portion of this experiment conducted tin 1998 was to refine and confirm data collected from the first part of the experiment, done in the previous reporting period. In the first experiment, 50% of the macaques inoculated intravaginally with 1000 TCID of HIV2287 become infected, and none of the macaques inoculated similarly with 100 TCID were infected. When inoculated intrarectally, 100% of the macaques became infected when inoculated with 1000 TCID, while none were infected when inoculated with 100 TCID. Two adult female M. nemestrina were selected and inoculated with 1000 TCID HIV-2287 intravaginally to confirm the 50% infection point; two male M. nemestrina were inoculated with 500 TCID intrarectally to confirm this dose as a 50% infecious dose. Only one of the intrarectally inoculated macaques became viremic to relatively high levels. T he infection of the intravaginally inoculated macaques was minimal and did not progress to disease. These four macaques were electively euthanatized at the end of the experiment and histopathology examination was made of all tissues. The remaining four macaques were not used for this experiment, and are being held for re-assignment. FUNDING NIH grant RR00166.